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CTEA Develops Rear Impact Guard

Jan 01, 2000

The Canadian Transportation Equipment Association (CTEA) has developed a generic rear impact guard for trailers. The guard complies with the energy-absorbing requirements of the US Department of Transportation (DOT) safety standards, specifically FMVSS 223 that the National Highway Transportation Safety Administration (NHTSA) has required since 26 January 1998.

The Canadian design project was undertaken by the CTEA so that individual manufacturers don't have to engineer their own guards for trailers that are sold or might be used in the United States, according to Al Tucker, general manager of the CTEA.

Canada also has requirements for the same type of energy-absorbing rear impact guard. In Ontario, for example, the rear impact guard is required on semitrailers over 48 feet long, as well as on doubles trains over 23 meters (75.5') long or a doubles box length over 18.5 m (60.7') long. It has applied to such trailers built since 26 January 1998.

The generic impact guard design was described by John R Billing, technician and project leader with the Canadian National Research Council (CNRC) and its Centre for Surface Transport Technology (CSTT). He spoke at the 36th annual meeting of the CTEA, held Oct 19 and 20 at the Hotel des Gouverneurs in Montreal, Quebec.

The generic guard uses a standardized yielding element in the supports for the bumper to achieve the required energy absorption, Billing said. The design meets the requirements of FMVSS 223 comfortably, he said, even allowing for variations in materials and fabrication.

The guard was designed using nonlinear finite element analysis and was qualified by full-scale testing in a rigid test fixture. Relatively good agreement was found between the analysis and testing.

The guard consists of a bumper that is attached to the rear end structure by two vertical supports. The lower part of each support yields in a controlled manner to provide the force displacement and energy absorption required by FMVSS 223. The upper part of each support must be integrated with the vehicle rear end structure so that it is much stiffer than the yielding component.

When fabricated according to the design guidelines, it does not have to be retested, Billing said. "Any manufacturer who elects not to use the test procedure spelled out in FMVSS 223 should be confident that their guard will pass if tested by NHTSA," Billing said.

Safety Standard 223 requires the impact guard to withstand a force of 50kN (11,240 lb) while deforming forward 125 mm (5") when struck near either the left or right side ends of the guard (P1) or in the center of the guard (P2). However, the most difficult test is the P3 location near the vertical supports that attach the horizontal impact guard beam to the trailer, said Billing. The P3 location (near the vertical supports) must withstand a force of 100 kN (22,480 lb) while moving forward 125 mm (5") at a controlled rate.

"The critical test for our design is the P3 test just outside the supports (25" from centerline) when the supports are narrowly spaced (at 36"), said Billing. "If a guard passes this test, it will pass any other P3 test at the support or just inside the support, and it will pass P1 and P2 tests. Therefore, for purposes of developing this impact guard design, it is necessary to do only the P3 test outside the supports, he said.

The generic impact guard can be made with the support spacing ranging from 914 to 1220 mm (36 to 48"). The support height can be from 203 to 610 mm (8 to 24"). The bumper itself is a

4 x 4" steel tube with 3/16" wall thickness. This steel tube is of 50 ksi steel. The test models were fabricated with steel ranging from 57 to 63 ksi yield point, but the design was adapted to use steel with a minimum strength of 50 ksi. "Using 50 ksi steel will still provide a 20% margin of passing the test successfully," Billing said.

CTEA generic impact guard can be attached to the trailer (or truck) by welding or bolting or both. The attachment must transfer a specified force applied to one of the supports at a point 2" above the bumper into the rear-end structure so there will be no permanent deformation of the attachment or the rear-end structure under the applied force.

Two safety standards apply to rear impact protection on trailers. The strength requirements and testing methods are spelled out in FMVSS 223, as stated above. FMVSS 224 requires that rear impact protection be mounted on all trailers and semitrailers having a gross vehicle weight rating of 10,000 lb or more manufactured since 26 January 1998. Exceptions are made for low-frame vehicles, trailers having the wheels positioned no more than 12" forward of the rear, pole trailers, and other difficult vehicle configurations.

The bumper must extend within 100 mm (4") of each side of the vehicle and be positioned no more than 22" above the ground and 12" forward of the trailer rear. The rear face of the bumper must be at least 100 mm (4") high.

The original idea for CTEA's development of a rear impact guard was conceived as a means to assist Canadian manufacturers in exporting their trailers to the United States and certifying that they meet all the US federal motor vehicle safety standards. However, the project expanded far beyond that concept, said Al Tucker.

"The success of this project represents a breakthrough in establishing the benefits of strategic alliances between Canadian and US trade associations," he said. "The Maintenance Council of the American Trucking Associations (TMC) and the National Truck Equipment Association (NTEA) invested in the research, and their membership now will benefit directly from the results."

The other 30 investors in the project are all Canadian trailer manufacturers, and these companies can be licensed to use the research work as a basis for certifying that their impact guards comply with FMVSS 223.